A. 1st degree heart block.
B. 3rd degree heart block.
C. 2nd degree heart block(Mobitz Type 1)
D. 2nd degree heart block(Mobitz Type 2)
Ans:D. 2nd degree heart block(Mobitz Type 2)
2nd degree heart block(Mobitz Type 2)
- Intermittent non-conducted P waves without progressive prolongation of the PR interval (compare this to Mobitz I).
- Constant P-R interval with missing QRS complexes.
- The RR interval surrounding the dropped beat(s) is an exact multiple of the preceding RR interval (e.g. double the preceding RR interval for a single dropped beat, treble for two dropped beats, etc)
- This dysrhythmia may present in a couple of different ways.
- A. QRS complexes occurring in a specific pattern in a ratio with the P waves. This is often referred to as 2:1 or 3:1 block depending upon the ratio of P waves to each QRS complex.
- B. QRS complexes occur in a more unstable, unpredictable manner.
- Mobitz II is usually due to failure of conduction at the level of the His-Purkinje system (i.e. below the AV node).
- Anterior MI (due to septal infarction with necrosis of the bundle branches).
- Idiopathic fibrosis of the conducting system (Lenegre’s or Lev’s disease).
- Cardiac surgery (especially surgery occurring close to the septum, e.g. mitral valve repair)
- Inflammatory conditions (rheumatic fever, myocarditis, Lyme disease).
- Autoimmune (SLE, systemic sclerosis).
- Infiltrative myocardial disease (amyloidosis, haemochromatosis, sarcoidosis).
- Drugs: beta-blockers, calcium channel blockers, digoxin, amiodarone.
- Mobitz II is much more likely than Mobitz I to be associated with haemodynamic compromise, severe bradycardia and progression to 3rd degree heart block.
- Onset of haemodynamic instability may be sudden and unexpected, causing syncope (Stokes-Adams attacks) or sudden cardiac death.
- Mobitz II mandates immediate admission for cardiac monitoring, backup temporary pacing and ultimately insertion of a permanent pacemaker.